This application relates to static VAR correctors (SVCs).
Static VAR correctors, also referred to as static VAR compensators, are electrical devices that provide reactance compensation to power transmission networks. SVCs are commonly used in various applications, including for example, regulating utility line voltage, improving network steady-state stability, and establishing near unity power factor on transmission lines.
Typically, an SVC includes a bank of controllable capacitors that can be individually switched in and out of circuit by a set of semiconducting switches (e.g., thyristors). Each switch is driven by electrical gating signals generated based on line conditions, allowing the corresponding capacitors to discharge and conduct in a controlled manner. When using thyristor switches that are capable of responding to gating signals within a sub-cycle (e.g., on the order of several milliseconds), an SVC is able to provide near-instantaneous reactance flow to compensate voltage/current fluctuations on utility networks.
The source impedance of a power system is usually inductive due to the presence of transformers and long transmission lines. Thus, when capacitors are switched onto transmission lines of the system, undesirable resonant conditions can be generated. Large amounts of resonant current may undesirably cause overheating in circuit components (e.g., capacitors) as well as current distortions in utility lines. Therefore, in some SVCs, a detuning reactor/inductor is provided to prevent capacitors from resonating with line inductance under normal operating conditions (e.g., line voltage within 95%˜105% of rated level). This reactor-capacitor coupling, however, does not prevent resonance from occurring under low voltage conditions, for example, when reactive power from SVCs are desired for rebuilding utility line voltage after a temporary power outage or voltage dip.